NUCLEATIONS DEPENDING ON RELATIVE DROP IN PRESSURE. 39 



Fig. 8 contains an extended comparison of the old curve for w 335 and 

 the new curve for w 345 , under the conditions which are given. In their 

 narrower variations the two curves are similar and the details already 

 specified for n 335 need not therefore be repeated for n 345 . Pronounced 

 maxima and minima will in particular be found coincident. 



The same will be observed in the case of fig. 9, where a larger scale is 

 introduced for n 335 . The question of greatest interest is now the com- 

 parison of mean data such as are given in table 14 in the lapse of time. 



The data for n 345 have been corrected for the effect of temperature 

 /, on the amount of water precipitated, by taking from the recent results 

 referred to the temperature coefficients dn/ndt, example of the values 

 for different relative drops being 



P/p= o.i 0.2 0.3 0.4 0.5 



io 3 dn/ndt= 14 18 23 27 30 



These data would not, however, seriously modify the trend of the 

 curves. 



The graph (fig. 10), which also contains these nucleations, shows that 

 the effect of temperature in the lapse of time has not been eliminated 

 by replacing the extreme variable (dp [TT ^i]) / (p rc) by the other 

 extreme variable dp/p. In other words, if the nucleation corresponding 

 to a fixed exhaustion op/p = 0.345 is studied in the lapse of time, the 

 successive nucleations* show a dependence on the temperature of the 

 fog chamber which can no longer be explained away. Both the details 

 and the general character of the graphs for n 345 follow the fluctuations 

 of temperature to an extent which may be estimated from the figure as 

 an increment of about 2000 nuclei per rise of temperature of i C. at 

 about 20 C. and for op/p = o. 345. Finally, there is no adequate reason 

 why the effect of cooling below a higher surrounding temperature should 

 be more efficient than the corresponding effect below a slightly lower 

 temperature ; for the rate of reheating would depend on the difference 

 of temperatures. 



21. Possible suggestions as to the temperature effect. To obtain a 

 suggestion as to the reason of the apparent increase of the size of col- 

 loidal nuclei with rise of temperature (cat. par.} effectively, therefore, 

 of their apparent increase in number at a given supersaturation, it 

 is expedient to recall the form of Helmholtz's modification of Kelvin's 

 vapor-pressure equation. If the ratio r of pressures at a convex surface 

 r and at a plane surface be p r /P m , R the gas constant of water vapor, 

 $ its absolute temperature, s the density, and T the surface tension of 

 the liquid, 



*American Journal, xxm, i97 IO . P- 2O 9- 



